The invention relates to a measuring device for measuring an illumination property of an illumination system, which is configured for two-dimensional irradiation of a substrate, arranged in an illumination plane, with illumination radiation. The invention furthermore relates to an arrangement with such a measuring device, an inspection apparatus for inspecting a surface of a substrate and a method for measuring an illumination system of the aforementioned type.
The prior art has disclosed inspection apparatuses for inspecting masks for microlithography, so-called mask inspection apparatuses, and inspection apparatuses for inspecting exposed wafers. The aerial image of the lithography mask to be inspected is measured in a mask inspection apparatus during a mask inspection in order to identify write errors of the mask or other mask defects. To this end, a mask inspection apparatus comprises an illumination system for generating illumination radiation radiated onto the mask to be inspected, and an inspection lens for imaging the mask structures on an inspection detector.
In order to obtain very precise measurement results, it is necessary to precisely set the illumination properties of the illumination system. Thus, it is necessary to ensure that both the homogeneity of the intensity distribution in the illumination plane of the illumination system, the so-called “illumination uniformity”, and the intensity distribution in the pupil of the illumination system satisfy predetermined specifications. In order to ensure this, the illumination uniformity and the intensity distribution in the pupil are firstly measured using a separate suitable measuring instrument in each case, and the illumination system is calibrated thereafter.
One option for calibration consists of individually loading the respective measuring instruments into the illumination plane. However, this requires a comparatively long period of time. If the measuring instruments are integrated into the inspection apparatus, it may be possible to save some time, but the spatial requirements for the measuring instruments in the inspection apparatus are significant. In order to ensure a high accuracy of the measurement results, a calibration of the individual measuring instruments is required in any case.